1. Field of the Invention
The present invention relates to a high speed line equalizer, and more particularly, to a high speed line equalizer constructed with an adaptive loop using a clock signal and equalizing a plurality of data channels using the adaptive loop, and a method thereof.
2. Description of the Background Art
Many researchers have currently focused to develop various types of high speed transmitting and receiving circuits to meet the demand of high speed communications increasingly required in data communications between boards or between systems.
However, when data are transmitted and received at high speed, a transmission speed and a transmission length are often limited due to a characteristic of a channel frequency. In more detail of characteristics of a typical channel, such a limitation increases in proportion to a square root of a frequency due to a skin effect. A frequency spectrum of a data transmitted from a transmitter exists within a wide frequency range, and thus, an input signal of a receiver often has a decreased signal integrity level due to the skin effect.
FIG. 1A is a diagram illustrating a waveform of a signal in a channel for describing the skin effect. As illustrated, a high frequency component has a lower amplitude level than a low frequency component. Such an inter-symbol interference is exhibited as an amplitude noise or a timing noise in an input signal of a receiver. As illustrated in FIG. 1B, an eye pattern of a received input signal is closed and thus, it is difficult to recover a correct signal at the receiver. This eye pattern closing event occurs more frequently when a channel length is longer or a data transmission rate increases.
A pre-emphasis method and an adaptive type equalizer have been introduced to overcome the inter-symbol interference problem. The pre-emphasis method amplifies a high frequency component considering that a signal of the high frequency component has a low amplitude level. The adaptive type equalizer adjusts a signal gain according to a frequency band in a manner to have a consistent amplitude level in all areas of the frequency band.
FIG. 2 is a configuration diagram briefly illustrating an equalizer used for the conventional pre-emphasis method.
The equalizer comprises a high pass filter HPF, a low pass filter LPF and an amplifier 1. The high pass filter HPF amplifies a high frequency component with respect to an input signal x[t] of a receiver. The low pass filter LPF amplifies a low frequency component with respect to the input signal x[t]. The amplifier 1 amplifies outputs of the high pass filter HPF and the low pass filter LPF to a certain gain level. At this point, an amplification rate of the high pass filter HPF is set to be high to have a consistent amplitude level according to a frequency band of a final output signal y[t].
FIG. 3 is a configuration diagram illustrating a conventional adaptive type high speed line equalizer.
The conventional adaptive type high speed line equalizer comprises an equalizing filter 10 and an adaptive loop 20. The equalizing filter 10 performs an equalizing operation according to a gain control signal. The adaptive loop 20 calculates amplitude levels of a high frequency component and a low frequency component of an output signal from the equalizing filter 10 and generates the calculated amplitude levels as a high frequency gain control signal and a low frequency gain control signal, respectively.
More particularly, the equalizing filter 10 comprises a high pass filter HP denoted with a reference numeral 11, a first amplifier 12 and a second amplifier 13. The high pass filter 11 passes only a high frequency component of an input signal ‘in.’ With respect to an output signal of the high pass filter 11, the first amplifier 12 adjusts a gain of the high frequency component according to a high gain control signal β. The second amplifier 13 adjusts gains of full band frequency components of the input signal ‘in’ according to a low gain control signal α.
The adaptive loop 20 comprises a third amplifier 25, a group of low pass filters 21 and 26, a group of high pass filters 22 and 27, a group of rectifiers 23, 24, 28, and 29, and a group of error amplifiers 31 and 32. The third amplifier 25 amplifies an output of the equalizing filter 10. More specifically, the third amplifier 25 amplifies a signal of a node A to a certain gain rate. The group of the low pass filters 21 and 26 separates low frequency components from the node A and another node B, respectively. The group of the high pass filters 22 and 27 separates high frequency components from the node A and the other node B. The group of the rectifiers 23, 24, 28, and 29 calculates a power level of each output signal from the group of the low pass filters 21 and 26 and the group of the high pass filters 22 and 27 and performs a rectifying operation. The group of the error amplifiers 31 and 32 amplifies errors of input signals of the low frequency components and the high frequency components, respectively.
Since the conventional adaptive type high speed line equalizer utilizes a self-gain adjustment mode, the low frequency gain is sufficient at the third amplifier 25 but insufficient at the equalizing filter 10. Therefore, controlling only the high frequency gain under this condition may cause the high frequency gain at the adaptive loop 20 to be converged into an erroneous value. For this reason, as illustrated in FIG. 3, it is generally necessary to have a low frequency loop comprising the second amplifier 13, the group of the low pass filters 21 and 26, the rectifiers 23 and 28 responsible for the low frequency components, and the error amplifier 31 responsible for the low frequency components.
Also, due to the co-existence of the high frequency loop and the low frequency loop, these two loops may struggle for each other. Hence, one of the high frequency loop and the low frequency loop may not function properly.
Since the adaptive loop 20 operates based on the self-gain adjustment mode, the adaptive loop 20 should be responsive according to an input signal. As a result, the adaptive loop 20 should deal with vast ranges of a wide band frequency. Accordingly, the implementation of a circuit for the conventional adaptive type high speed line equalizer may get complicated. Particularly, when there are multiple channels, the equalizing filter 10 and the adaptive loop 20 are additionally necessary for every input channel. This additional installation of the input channels may increase the circuit area and power consumption.